During the lifetime of oil and gas wells, situations arise where there is a need for the introduction of a material with sealing properties. Such situations include plugging and abandonment (P&A), lost circulation, and isolation of zones in the well. Plugging and abandonment operations are generally carried out in situations where the well does not produce enough hydrocarbons to be profitable, or in situations where the well has neared the end of its lifetime and is depleted of hydrocarbons. Temporary plugging of wells is typically carried out during maintenance operations of the well. Lost circulation describes the situation where drilling fluid is lost in the formation and flows into the formation instead of returning through the annulus and to the surface. Zonal isolation is carried out to prevent the cross-flow of fluids between geological layers and to reduce the volume of produced water.
In the prior art, cement is commonly used as a sealant material. The disadvantages connected to the use of ordinary cement is long setting time, insufficient mechanical properties for certain applications, poor penetration capability in formations, susceptibility to cracking, and poor resistance towards certain chemicals, in particular acids. There is a need in the art for a material that can improve the properties of ordinary cement for the purposes mentioned herein.
The applicant has previously patented a technology (U.S. Pat. No. 6,082,456, NO310941B1) that seeks to overcome many of the disadvantages exhibited by the use of cement as a sealant material in oil and gas wells. The material described in the patents comprises a prepolymer, at least one vinylic monomer, an initiator, an inhibitor and optionally, a filler, hereafter described as “the prepolymer mixture”. The prepolymer is in the form of at least a partially unsaturated polyester or epoxy vinylester. The material described in the referred patents is particularly advantageous compared to cement with respect to its short setting time.